EVAP System Components

The EVAP system includes the following components:
^ Fuel Tank
^ Fuel Level Sensor
^ Vent Solenoid (Fresh Air Solenoid)
^ Fuel Tank Pressure Sensor
^ Fuel pipes and hoses
^ Vapor lines
^ Fuel Cap
^ Evaporative Emission Canister
^ Purge lines
^ Purge Valve Solenoid
^ Enhanced Evaporative Emission ([1][2]EVAP) Service Port
^ Throttle Body
^ Powertrain Control Module (PCM)
^ Fuel Tank
The fuel vapor generated inside the fuel tank is released to the canister for containment. The fuel tank is made of High Density Polyethylene (HDPE) which is a high tech plastic material.

^ Fuel Level Sensor
The fuel level sensor is an input to the PCM for the enhanced evaporative system diagnostic. The fuel level affects the rate of charge in the air pressure in the EVAP system. The fuel level sensor input to the PCM is used to determine if the fuel level in the tank is correct to run the [1][2]EVAP diagnostic tests. To ensure sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15 percent and 85 percent.

^ Vent Solenoid (Fresh Air Solenoid)
The Vent Solenoid (Fresh Air Solenoid) is the device that allows fresh air into the purge canister. The vent solenoid is an on/off device which is normally open to allow fresh air into the purge system. For diagnostic testing, the vent solenoid is closed and vacuum decay tests are run on the system. Consequently, the vent solenoid serves a dual purpose of supplying fresh air and acting as a diagnostic switch.

^ Fuel Tank Pressure Sensor
The fuel tank pressure sensor is used to detect small leaks in the evaporative emission system. The diagnostic is based on a vacuum decay strategy. At an appropriate time engine vacuum is used to draw a small vacuum on the entire evaporative emission system by mechanically sealing off the designed vent path.

^ Fuel Pipes and Hoses
The fuel pipes and hoses carry the fuel to the various EVAP system components.

^ Vapor Lines
The fuel vapor lines carry the fuel vapors to the various EVAP system components

NOTE: Use a fuel tank filler pipe cap with the same features when a replacement is necessary. Failure to use the correct fuel tank filler pipe cap can result in a serious malfunction of the fuel system.

^ Fuel Cap
The fuel cap is a screw-type cap that screws on to the fuel tank filler pipe. A loose or missing fuel cap will set a DTC.

^ [1][2]EVAP Emission Canister
The rectangular designed canister is filled with activated carbon that stores vapor transferred from the fuel tank. Integral to the canister is a trap which collects any liquid fuel (condensed vapor) from entering and contaminating the charcoal bed. The liquid is purged back to the tank whenever there is a vacuum exerted on the tank. The EVAP charcoal canister also has a volume compensator that maintains a tightly packed charcoal bed as the canister expands and contracts.

^ EVAP Canister Purge Solenoid
The EVAP canister purge solenoid allows manifold vacuum to purge the canister. The EVAP canister purge solenoid is normally closed. The Powertrain Control Module (PCM) supplies a ground to energize the EVAP canister purge solenoid valve (purge on). The EVAP canister purge solenoid control is Pulse Width Modulated (PWM) or turned on and off several times a second. The PCM controlled PWM output is command when the appropriate conditions have been met:
^ Engine coolant temperature above 25 degrees C (77 degrees F)
^ After the engine has been running about 2 1/2 minutes on a cold start or 30 seconds on a warm start.
^ The vehicle is operating in closed loop fuel control.
^ Canister purge PWM duty cycle varies according to operating conditions determined by mass air flow, fuel trim, and intake air temperature. Canister purge will be disabled if TP angle increases to above 70 percent. Canister purge will be re-enabled when TP angle decreases below 66 percent.

The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay.

The fuel level sensor input to the PCM is used to determine if the fuel level in the tank is correct to run the [1][2]EVAP diagnostic tests. To ensure sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15% and 85%.

The PCM monitors system vacuum level via the fuel tank pressure sensor input.

^ Purge Lines
The purge lines carry the fuel vapors to the various EVAP system components.

^ Enhanced Evaporative Emission ([1][2]EVAP) Service Port
The Enhanced Evaporative Emission (EVAP) Service Port is located between the purge valve solenoid and the EVAP emission canister. The service port is identified by a green color cap. The port contains a schrader valve and fittings in order to allow the connection of the service tool kit Enhanced EVAP Pressure Purge Diagnostic Car J 41413.

^ Throttle Body
The throttle body provides a intake manifold vacuum signal to purge the canister of its stored vapor. The purge ports are always exposed to the manifold side of the throttle blades, making intake vacuum available to purge the canister. EVAP canister purge is controlled by the PCM via the purge solenoid.

^ Powertrain Control Module (PCM)
The PCM commands the purge valve solenoid to open and allow engine vacuum to draw stored fuel vapors from the canister into the throttle body.